JP2008136851A - Magnetic resonance imaging apparatus and magnetic resonance imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take an image of stable quality while preventing an image degradation caused by changes in heart rate. <P>SOLUTION: An acquisition unit comprising a gradient magnetic field power source 3, a transmitter 7, a selective circuit 8, a receiver 9 and a data collection section 11b, acquires magnetic resonance data relating to magnetic resonance in every data group on a subject 200. A main control unit 11g controls the acquisition unit to collect the data for a plurality of data groups during a collection period which is set from a starting time phase of a cardiac cycle of the subject 200, and then determines, among the data acquired by the acquisition unit, the data acquired during an ineffective period which is set from the ending time phase of the cardiac cycle after completion of the cardiac cycle during which the magnetic resonance is obtained as ineffective data, and the data acquired during a period other than the ineffective period as effective data. A reconstitution unit 11c reconstitutes an image regarding the subject 200 by using the effective data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging (MRI) apparatus and a magnetic resonance imaging method for imaging the subject based on magnetic resonance data related to magnetic resonance in the subject.

  In cardiac imaging by MRI, it is desirable to suppress degradation of image quality due to heart motion. In this manner, it is important to suppress deterioration in image quality due to the movement of the heart, particularly in imaging methods that require high spatial resolution, such as coronary artery imaging and myocardial delayed contrast imaging. As an imaging method adapted to such needs, there is known a method of selectively collecting data during a period in which the heartbeat is small in the cardiac cycle (see, for example, Non-Patent Document 1). In this method, data collection is performed in a period determined from a preset delay time and data collection time (window time) starting from an R wave obtained from the electrocardiographic waveform of the subject.

  FIG. 5 is a diagram showing an example of a pulse sequence in the MRI method for collecting data of a specific cardiac time phase in the cardiac cycle. Data collection is performed during a period from the start time Ts when the heart motion is reduced to the end time Te when the heart starts moving again. However, normally, the time point when the delay time Td has elapsed since the R wave appeared from the electrocardiographic waveform of the subject is set as the start time point Ts. Further, a time point when the window time Tw has elapsed from the start time point Ts is set as an end time point Te. As a result, data is collected only during a period in which there is little heart movement, generally called a ventricular diastole or slow inflow. Note that the period in which the heart moves little is a period in which the change in the left ventricular volume is small as shown in FIG. 5 (the period in which the graph of the left ventricular volume is flat). By collecting data during this period, it is possible to suppress deterioration in image quality due to the influence of heart motion.

  As shown in FIG. 5, pre-pulse irradiation is performed during a period until the delay time Td elapses. The prepulse is, for example, an inversion pulse, a T2-weighted preparation pulse, a magnetization transfer contrast (MTC) pulse, a dummy shot, a fat suppression pulse, or a pulse for detecting respiratory movement. The inversion pulse is a pulse for improving the contrast of an image in the case of coronary artery imaging or myocardial delayed contrast imaging. The T2-weighted preparation pulse is a pulse for T2-weighted. The MTC pulse is a pulse for increasing contrast by using magnetization transfer of two or more spin systems. The dummy shot is a pulse for promoting the arrival of the nuclear spin to the steady state. The fat suppression pulse is a pulse for suppressing a fat signal.

It is known that the length of a period with less heartbeat varies according to the heart rate of the subject. For this reason, it is preferable to set an appropriate delay time Td and window time Tw for each subject in order to improve image quality. In view of this, a method for supporting setting of an appropriate delay time Td and window time Tw for each subject has been proposed (see Non-Patent Document 2). In this method, it is possible for the operator to visually determine a period during which there is little heartbeat by performing, for example, a short cine imaging in which the motion of the heart is known.
Stuber M et al, "Submillimeter Three-dimensional Coronary MR Angiography with Real-Time Navigator Correction: Comparison of Navigator Locations.", Radiology 1999; 212: 579-587 Plein S et al, "Three-Dimensional Coronary MR Angiography Performed with Subject-Specific Cardiac Acquisition Window and Motion-adopted Respiratory Gating."AJR; 180: 505-512,2003 Yukio Kuribayashi / Satoshi Sakuma, MDCT and MRI of cardiovascular disease, Medical School, September 2005, P.C. 16

  The number N of data lines that can be collected within one heartbeat is obtained from the pulse sequence repetition time TR and the window time Tw by the following equation.

N = Tw / TR
For example, consider the case of performing three-dimensional data collection. If the number of slices, that is, the slice encoding number Kz is 60 and the number of matrixes Ky in the phase encoding direction is 120, the required number of data lines can be obtained as 7200 lines by the following equation.

Kz x Ky = 60 x 120 = 7200
Assuming that the window time Tw with little heart movement within one cardiac cycle is 100 msec, if the repetition time TR is 5 msec, the number N of data lines that can be collected within one heartbeat is obtained as 20 lines from the following equation.

N = 100/5 = 20
The heart rate required to collect all the data lines necessary for image reconstruction is calculated as 360 beats from the following equation.

7200/20 = 360
If one heartbeat is 1 second, data collection is completed in 360 seconds, that is, 6 minutes. However, in general, it is necessary to consider the body movement caused by breathing of the subject in addition to the movement of the heart, and in many cases, a method of selectively collecting data with little influence of the body movement caused by breathing is used together. In this case, the actually required data collection time is longer than this.

  The method proposed in Non-Patent Document 2 is considered to work effectively when the heart rate of the subject is extremely stable. However, the heart rate of the subject may change during the long data collection period as described above. If the heart rate increases, the duration of the time phase in which the heart moves little is shortened, and the appropriate value of the window time Tw is also shortened. For example, it is assumed that the window time Tw as shown in FIG. 6 is set in accordance with the RR interval Trr1 shown in FIG. At this time, when the RR interval is shortened to Trr2 shown in FIG. 6, the time point at which the heart motion increases changes from Te1 to Te2. In this case, the heart moves greatly during the data collection period. In the case of FIG. 6, the data collected in the period Pa is greatly influenced by the heartbeat, which causes blurring in the reconstructed image.

  The present invention has been made in consideration of such circumstances, and the object of the present invention is to prevent image quality deterioration due to a change in heart rate and to perform imaging with stable image quality. It is in.

  The magnetic resonance imaging apparatus according to the first aspect of the present invention is an acquisition means for acquiring magnetic resonance data related to magnetic resonance in a subject for each data line, and acquisition determined based on a start time of the cardiac cycle of the subject. Among the magnetic resonance data acquired by the acquisition means, the control means for controlling the acquisition means so as to collect magnetic resonance data for one or a plurality of unit data groups in a period, the magnetic resonance data A unit data group in which all data is acquired in a period other than the invalid period, with the data relating to the unit data group acquired at least in part in the invalid period determined based on the end point of the cardiac cycle in which acquisition is performed as invalid data Determination means for determining the data relating to the subject as valid data, and means for reconstructing an image relating to the subject using the valid data.

  The magnetic resonance imaging apparatus according to the second aspect of the present invention is an acquisition means for acquiring magnetic resonance data related to magnetic resonance in a subject for each data line, and acquisition determined based on the start time of the cardiac cycle of the subject. Among the magnetic resonance data acquired by the acquisition means and the control means for controlling the acquisition means so as to collect magnetic resonance data for a plurality of data lines in a period, acquisition of the magnetic resonance data is performed. Data relating to data lines acquired at least in part during the invalid period determined based on the end point of the given cardiac cycle are used as invalid data, and data relating to data lines obtained during all periods other than the invalid period are used as valid data Determination means for determining, and means for reconstructing an image relating to the subject using the valid data.

  According to a third aspect of the present invention, there is provided a magnetic resonance imaging apparatus comprising: acquisition means for acquiring magnetic resonance data relating to magnetic resonance in a subject for each data line; and collection determined based on a start time of the subject's cardiac cycle. Among the magnetic resonance data acquired by the acquisition means, the control means for controlling the acquisition means so as to collect magnetic resonance data for one or a plurality of slice encodings in a period, of the magnetic resonance data Data related to slice encoding acquired at least partially during the invalid period determined based on the end point of the cardiac cycle in which the acquisition was performed, and data related to slice encoding acquired all during the period other than the invalid period Determination means for determining as valid data, and reconstructing an image related to the subject using the valid data And a stage.

  In the magnetic resonance imaging method according to the fourth aspect of the present invention, magnetic resonance data relating to magnetic resonance in the subject is acquired for each data line, and the acquisition period is determined based on the start time of the subject's cardiac cycle. The acquisition is controlled so as to collect magnetic resonance data for a plurality of data lines, and is determined based on the end point of the cardiac cycle at which the magnetic resonance data is acquired among the acquired magnetic resonance data The data related to the data line acquired during the invalid period is determined as invalid data, the data related to the data line acquired during a period other than the invalid period is determined as valid data, and the image related to the subject is determined using the valid data. Reconfigure.

  In the magnetic resonance imaging method according to the fifth aspect of the present invention, magnetic resonance data relating to magnetic resonance in the subject is acquired for each data line, and the acquisition period is determined based on the start time of the subject's cardiac cycle. The acquisition is controlled to collect magnetic resonance data for one or a plurality of slice encodings, and among the acquired magnetic resonance data, at the end of the cardiac cycle at which the magnetic resonance data was acquired The data related to the slice encoding acquired at least partially in the invalid period determined based on the invalid data is determined as the invalid data, and the data related to the slice encoding acquired in all other periods than the invalid period is determined as the valid data, and the valid data is used. Then, an image relating to the subject is reconstructed.

  According to the present invention, it is possible to prevent image quality deterioration due to a change in heart rate and perform imaging with stable image quality.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an MRI apparatus 100 according to the present embodiment. The MRI apparatus 100 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a bed 4, a bed control unit 5, RF coil units 6a, 6b, and 6c, a transmission unit 7, a selection circuit 8, a reception unit 9, An ECG unit 10 and a computer system 11 are provided.

  The static magnetic field magnet 1 has a hollow cylindrical shape and generates a uniform static magnetic field in an internal cylindrical space. For example, a permanent magnet or a superconducting magnet is used as the static magnetic field magnet 1.

  The gradient magnetic field coil 2 has a hollow cylindrical shape and is disposed inside the static magnetic field magnet 1. The gradient magnetic field coil 2 is a combination of three types of coils corresponding to the X, Y, and Z axes orthogonal to each other. The gradient magnetic field coil 2 generates a gradient magnetic field in which the above three types of coils are individually supplied with current from the gradient magnetic field power supply 3 and the magnetic field strength is inclined along the X, Y, and Z axes. The Z-axis direction is the same as the static magnetic field direction, for example. A slice selection gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr are formed by combining the gradient magnetic fields of the X, Y, and Z axes. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used for changing the frequency of the magnetic resonance signal in accordance with the spatial position.

  The couch 4 is driven by the couch controller 5 and moves the top plate 4a in the longitudinal direction (left-right direction in FIG. 1) and up-down direction. Usually, the bed 4 is installed such that the longitudinal direction thereof is parallel to the central axis of the static magnetic field magnet 1. The subject 200 is inserted into the cavity (diagnostic space) of the gradient magnetic field coil 2 by moving the top plate 4a while being placed on the top plate 4a.

  The RF coil unit 6a is configured by housing one or more coils in a cylindrical case. The RF coil unit 6 a is disposed inside the gradient magnetic field coil 2. The RF coil unit 6a receives a high frequency pulse (RF pulse) from the transmitter 7 and generates a high frequency magnetic field.

  The RF coil units 6b and 6c are placed on the top plate 4a, built in the top plate 4a, or attached to the subject 200. And at the time of imaging | photography, it inserts in the space for a diagnosis with the subject 200. FIG. Array coils are used as the RF coil units 6b and 6c. That is, each of the RF coil units 6b and 6c includes a plurality of element coils. The element coils provided in the RF coil units 6b and 6c each receive a magnetic resonance signal radiated from the subject 200. The output signals of the element coils are individually input to the selection circuit 8. The receiving RF coil unit is not limited to the RF coil units 6b and 6c, and various types of RF coil units can be arbitrarily attached. One or three or more RF coil units for reception may be attached.

  The transmitter 7 supplies an RF pulse corresponding to the Larmor frequency to the RF coil unit 6a.

  The selection circuit 8 selects some of a number of magnetic resonance signals output from the RF coil units 6b and 6c. Then, the selection circuit 8 gives the selected magnetic resonance signal to the reception unit 9. The computer system 11 instructs which channel the selection circuit 8 should select.

  The receiving unit 9 includes a plurality of processing systems including a pre-stage amplifier, a phase detector, and an analog / digital converter. Magnetic resonance signals selected by the selection circuit 8 are respectively input to the processing systems of these multiple channels. The pre-stage amplifier amplifies the magnetic resonance signal. The phase detector detects the phase of the magnetic resonance signal output from the preamplifier. The analog-digital converter converts the signal output from the phase detector into a digital signal. The receiving unit 9 outputs a digital signal obtained by each processing system.

  The ECG unit 10 includes an ECG sensor that attaches to the body surface of the subject 200 and detects an ECG signal as an electrical signal. The ECG unit 10 performs various processes including a digitization process on the signal output from the ECG sensor and outputs the processed signal to the computer system 11.

  The computer system 11 includes an interface unit 11a, a data collection unit 11b, a reconstruction unit 11c, a storage unit 11d, a display unit 11e, an input unit 11f, and a main control unit 11g.

  The interface unit 11a is connected to the gradient magnetic field power source 3, the bed control unit 5, the transmission unit 7, the reception unit 9, the selection circuit 8, and the like. The interface unit 11 a inputs and outputs signals exchanged between the connected units and the computer system 11.

  The data collection unit 11b collects digital signals output from the reception unit 9. The data collection unit 11b stores the collected digital signal, that is, magnetic resonance data in the storage unit 11d.

  The reconstruction unit 11c performs post-processing, that is, reconstruction such as Fourier transform, on the magnetic resonance data stored in the storage unit 11d, and obtains spectrum data or image data of the desired nuclear spin in the subject 200. Ask. At the time of electrocardiogram synchronous imaging, the reconstruction unit 11c uses only the magnetic resonance data determined as valid data by the main control unit 11g for reconstruction.

  The storage unit 11d stores magnetic resonance signal data and spectrum data or image data for each subject.

  The display unit 11e displays various information such as spectrum data or image data under the control of the main control unit 11g. As the display unit 11e, a display device such as a liquid crystal display can be used.

  The input unit 11f receives various commands and information input from the operator. As the input unit 11f, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard can be used as appropriate.

  The main control unit 11g has a CPU, a memory, and the like, and comprehensively controls the MRI apparatus 100 of the present embodiment. The main controller 11g has the following functions in addition to the well-known functions for realizing the operation of the MRI apparatus 100. One of the functions is that the gradient magnetic field power supply 3, the transmission unit 7, and the selection are selected so as to collect magnetic resonance data for a plurality of data lines in a collection period determined based on the start time of the cardiac cycle of the subject 200. The circuit 8, the receiving unit 9, the data collecting unit 11b, and the like are controlled. One of the above functions determines the magnetic resonance data as invalid data or valid data based on whether the magnetic resonance data was acquired during the invalid period. One of the functions controls the gradient magnetic field power source 3, the transmission unit 7, the selection circuit 8, the reception unit 9, the data collection unit 11b, and the like so that magnetic resonance data related to the same data line as the invalid data is acquired again.

  Next, the operation of the MRI apparatus 100 will be described.

  In the following, a case will be considered where three-dimensional data acquisition is performed with ECG synchronization using a pulse sequence with a repetition time TR of 5 msec, where the slice encoding number Kz is 60 and the matrix number Ky in the phase encoding direction is 120. According to the setting of 100 msec as the window time Tw, it was planned to collect data for all 7200 dera lines by collecting data for 20 data lines per cardiac cycle over 360 cardiac cycles. I will do it. Furthermore, although the situation differs from the actual cardiac cycle fluctuation, for the sake of simplicity of explanation, the case where the RR interval in two consecutive cardiac cycles in 360 cardiac cycles is lower than the other cardiac cycles. Think.

  FIG. 2 is a timing chart showing an example of the relationship between the electrocardiogram waveform of the subject 200 and the execution timing of data collection. (A) in FIG. 2 shows only the generation timing of the R wave in the electrocardiogram waveform. The RR interval is Trr1 for the 358 cardiac cycles of the 360 cardiac cycles planned for data collection as described above, and the RR intervals for the remaining two cardiac cycles are Trr2 and Trr3, respectively. These RR intervals have a relationship of Trr1> Trr2> Trr3.

  FIG. 2B shows the execution timing of data collection. As shown in (b), within each cardiac cycle, 20 data lines from the time when the delay time Td has elapsed since the R wave was generated, regardless of the size of the RR interval in that cardiac cycle. Data collection. This data collection is performed by, for example, the well-known operation of the gradient magnetic field power source 3, the transmission unit 7, the selection circuit 8, the reception unit 9, the data collection unit 11b, and the like under the control of the main control unit 11g.

  When the next R wave is generated in the electrocardiogram waveform, the main controller 11g starts measuring the delay time Td in order to determine the start timing of data collection in the cardiac cycle starting from the next R wave. At the same time, the main control unit 11g determines validity / invalidity of the magnetic resonance data collected in the cardiac cycle terminated by the R wave.

  By the way, it is known that when the heart rate of the subject 200 changes, the RT interval (systole) does not change so much and the TR interval (diastolic phase) expands and contracts (non-patented). Reference 3). Therefore, when the heart rate increases, the end portion of the preset data collection window starts in the atrial systole where the heart moves greatly, and in the extreme case, it spans the next cardiac cycle. As described above, the magnetic resonance data collected in the period across the boundary between the atrial systole and the cardiac cycle is greatly affected by the heartbeat. Therefore, in the present embodiment, within one cardiac cycle, a period later than the time point that goes back a predetermined time (hereinafter referred to as backward delay) Tbd from the time when the R wave at the end of the cardiac cycle occurs. Invalid period. The magnetic resonance data related to the data line collected at least during this invalid period is regarded as invalid data. Also, magnetic resonance data relating to data lines that are collected outside the invalid period are valid data.

  For this determination, the main control unit 11g measures the RR interval Trr between the newly generated R wave and the previous R wave, and determines whether Td + Tw is smaller than Trr−Tbd. . When Td + Tw is smaller than Trr−Tbd, all the magnetic resonance data collected during the cardiac cycle is obtained outside the invalid period, that is, during a period when there is little heart movement. judge.

  (C) of FIG. 2 specifically shows an electrocardiogram waveform, data collection execution timing, and collected magnetic resonance data in a cardiac cycle in which the RR interval is Trr1. In this cardiac cycle, Td + Tw is smaller than Trr1-Tbd. Accordingly, any 20 lines of magnetic resonance data collected in this cardiac cycle are valid data.

  On the other hand, when Trr is shortened due to an increase in the heart rate during imaging and Td + Tw exceeds Trr−Tbd, at least a part of the magnetic resonance data is obtained in the atrial systole where the heart motion is large. Therefore, magnetic resonance data relating to data lines collected even in part during the invalid period is invalid data, and magnetic resonance data relating to other data lines is valid data. The nth (1 ≦ n ≦ 20) data line acquired in each cardiac cycle is acquired at a time of approximately Td + n · TR from the previous R wave. Therefore, when Td + n · TR <Trr−Tbd is established, the magnetic resonance data regarding the nth acquired data line is set as effective data. If the above relationship does not hold, the magnetic resonance data related to the n-th acquired data line is set as invalid data. Note that the line number or phase encoding amount of the data line regarded as invalid data is recorded as information on the uncollected data line.

  FIG. 2D specifically shows an electrocardiogram waveform, data collection execution timing, and collected magnetic resonance data in a cardiac cycle in which the RR interval is Trr2 and Trr3. In the cardiac cycle in which the RR interval is Trr2, Td + Tw is smaller than Trr2-Tbd. In the cardiac cycle in which the RR interval is Trr3, Td + Tw is smaller than Trr3-Tbd. In the cardiac cycle in which the RR interval is Trr2, the magnetic resonance data for the four data lines hatched in FIG. 2 are hatched in FIG. 2 in the cardiac cycle in which the RR interval is Trr3. The magnetic resonance data for 8 data lines shown in FIG. Note that the magnetic resonance data acquired in the data lines that are not hatched in FIG. 2 are valid data.

  The valid data is stored in the storage unit 11d. The invalid data may be stored in the storage unit 11d separately from the valid data, or may be discarded at this point.

  These data lines related to invalid data are hereinafter referred to as uncollected data lines. Regarding the uncollected data lines, after the scheduled data collection (for example, collection of magnetic resonance data for each of the data lines of the number of phase encoding times the number of slice encodings) is completed, the data lines are continuously collected in synchronization with the electrocardiogram waveform. Can do.

  Specifically, even if invalid data occurs, data is collected as originally planned during 360 cardiac cycles. In other words, the data collection for the required 7200 data lines is performed. After this is completed, the main control unit 11g checks whether or not the line number or phase encoding amount of the uncollected data line is recorded. If this is recorded, the main controller 11g starts re-acquisition of magnetic resonance data regarding the corresponding data line.

  The reacquisition is performed in the same manner as the normal data collection described above for each of the uncollected data lines in which the line number or the phase encoding amount is recorded. If the number of uncollected data lines is 21 or more, the main control unit 11g plans recollection so that 20 data lines are allocated to one cardiac cycle. In the example of FIG. 2, there are a total of 12 uncollected data lines, so this is planned and collected to be collected in one cardiac cycle as shown in FIG. For the data acquired by this recollection, the main control unit 11g performs the validity / invalidity determination in the same manner as described above. Re-collection is repeated until there is no magnetic resonance data determined as invalid data.

  When there is no magnetic resonance data determined as invalid data, the storage unit 11d has valid data for all 7200 data lines. The reconstruction unit 11c reconstructs an image using this valid data.

  Thus, according to the present embodiment, even if a change occurs in the heart rate of the subject, reconstruction is performed using only the magnetic resonance data acquired during a period in which the heart motion is small. Thereby, it is possible to perform imaging with stable image quality without being affected by the movement of the heart.

  By the way, the window time Tw may be set so that a sufficient time margin remains from the end of data collection until the heart motion increases in order to reliably reduce the influence of the heart motion. It is common. That is, conventionally, data collection has been performed using only a part of a period in which the heart motion is small. For this reason, the number of data lines per cardiac cycle is reduced, leading to an increase in imaging time. On the other hand, according to the present embodiment, if the window time Tw is set longer than the conventional one without considering the above margin, the number of data lines per one cardiac cycle is improved during a period when the heart rate is low. Therefore, the imaging time can be shortened. Furthermore, in anticipation of a decrease in the heart rate, the window time Tw is set to a value larger than the time width of the period in which the heart motion is small at the time of setting, thereby further reducing the imaging time. It is also possible to measure. In other words, it is planned in advance to set a data collection window longer than the period during which the heart motion is confirmed before imaging, and to collect a larger number of data lines within one cardiac cycle. In this way, when the heartbeat of the subject 200 becomes longer than the measurement before imaging, n satisfying Td + n · TR> Trr−Tbd is increased, so that there is little movement of the heart confirmed before imaging. More data can be collected than the number of data lines that can be collected in a period. If the heart rate of the subject 200 is often long, the number of data that can be collected can be increased accordingly, and the total imaging time for collecting all data can be shortened.

  Prior to data collection in each cardiac cycle, prepulse irradiation is performed as shown in FIG. According to the present embodiment, since the delay time Td is constant regardless of the RR interval, the pre-pulse irradiation may be performed at a constant timing based on the R wave.

  This embodiment can be variously modified as follows.

  Recollection of magnetic resonance data relating to uncollected data lines can be performed by dynamically determining timing during imaging. That is, an uncollected data line recorded in a certain cardiac cycle can be planned to be collected after the collection of the data line scheduled for a subsequent cardiac cycle. That is, when the heart rate decreases and the RR interval Trr extends in the subsequent cardiac cycle, it is possible to collect magnetic resonance data of uncollected data lines from the beginning in the cardiac cycle. FIG. 3 is a diagram showing the characteristics of the data collection procedure of this modification. There are 8 uncollected data lines in the first cardiac cycle in FIG. This uncollected data line is planned to be collected again after data collection for the originally planned data line in the next cardiac cycle. In the example of FIG. 3, the RR interval has been extended from Trr11 to Trr12, so that re-collection for four uncollected data lines has been successful. However, collection of four uncollected data lines is still possible. It is invalid. After the data collection for the originally planned data line in the third cardiac cycle in FIG. 3, it is planned to re-collect the above four lines that are still uncollected. In the example of FIG. 3, since the RR interval is sufficiently large as Trr13, the recollection of four uncollected data lines has succeeded. By doing in this way, it is possible to perform re-collection on uncollected data lines while collecting data on originally planned data lines. If the number of uncollected data lines increases because the state in which the heart rate has increased continues, recollection of these uncollected data lines may not be completed during one cardiac cycle. Therefore, the number of recollection lines to be attempted in one cardiac cycle may be limited to a predetermined number, and it may be planned to divide and recollect in a plurality of cardiac cycles.

  If the uncollected data line is a data line near the end of the k space, that is, a data line corresponding to a high spatial frequency, the magnetic resonance data of the data line does not contribute to the image contrast. Therefore, the re-collection of magnetic resonance data of such data lines may not be performed. In this case, the data line is reconfigured by filling with 0 data. The range of data lines to be recollected may be fixed, or may be arbitrarily set according to the operator's specification. The range of the data line to be recollected should be specified according to the spatial frequency and the phase encoding amount. Also, if the data line closer to the center of the k space is planned to acquire data at an earlier timing of each cardiac cycle, the probability that an uncollected data line becomes a data line near the end of the k space is improved. Efficient data collection with a reduced number of collected data lines can be performed. Even when the data line that is not important for the reconstruction of the image to be obtained is other than the data line in the vicinity of the end of the k space, the data line may be excluded from the recollection target.

  Re-collection may be performed not only on the uncollected data lines but also on the surrounding data lines, and the reconstruction may be performed using the magnetic resonance data regarding the data lines obtained in duplicate. In this way, the S / N of the reconstructed image can be improved.

  The backward delay Tbd may be determined by multiplying the RR interval of each cardiac cycle by a predetermined coefficient less than 1. In this case, the backward delay Tbd changes every cardiac cycle.

  An ECG waveform measured by the ECG unit 10 is displayed on the setting screen for setting the delay time Td, window time Tw, or backward delay Tbd by the operator, and designation of each time is accepted according to the ECG waveform. May be.

  The unit data group that is a target for determining whether or not the magnetic resonance data is invalid is not limited to one data line, and may be arbitrary. For example, when a multi-echo method such as the fast spin echo method is employed as the pulse sequence, it is necessary to collect magnetic resonance data for one slice encoding within one cardiac cycle. In the case of two-dimensional imaging, it is desirable to collect magnetic resonance data for one slice within one cardiac cycle in order to reduce artifacts. Under such circumstances, imaging may be planned so as to collect magnetic resonance data for one or a plurality of slice encodings within one cardiac cycle. In this case, the unit data group is magnetic resonance data for one slice encoding.

  FIG. 4 is a timing diagram showing an example of the relationship between the electrocardiogram waveform and the data collection execution timing when magnetic resonance data for one slice encoding is collected at the window time Tw. FIG. 4 shows a case where data collection for Kz slice encoding is performed by performing one slice encoding per one cardiac cycle over the Kz cardiac cycle. With only two cardiac cycles of the Kz cardiac cycle, the RR interval is Trr32 and Trr33 different from Trr31 in the other cardiac cycles. These RR intervals have a relationship of Trr31> Trr32> Trr33.

  In FIG. 4, Td + Tw is smaller than Trr31−Tbd or Trr32−Tbd. Therefore, any slice-encoded magnetic resonance data collected in this cardiac cycle is valid data. However, since Td + Tw is larger than Trr33−Tbd, all of the slice-encoded magnetic resonance data collected in this cardiac cycle is invalid data. As for the slice encoding that is regarded as invalid data, after the data collection for the Kz slice encoding is finished as originally planned, the data for one slice encoding is collected again.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The figure which shows the structure of the MRI apparatus 100 which concerns on one Embodiment of this invention. The timing diagram which showed an example of the relationship between the electrocardiogram waveform of the subject 200 and the execution timing of data collection. The figure which shows the characteristic of the procedure of the data collection in the deformation | transformation embodiment of this invention. Timing chart showing an example of the relationship between the electrocardiogram waveform and the data collection execution timing when magnetic resonance data for one slice encoding is collected in the window time Tw The figure which shows an example of the pulse sequence in the MRI imaging method which collects the data of the specific cardiac time phase in a cardiac cycle like coronary artery imaging or myocardial delay angiography. The figure which shows a mode that the change of a subject's heart rate influences data collection.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... MRI apparatus, 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Gradient magnetic field power supply, 4 ... Bed, 5 ... Bed control part, 6a, 6b, 6c ... Coil unit, 7 ... Transmission part, 8 ... Selection Circuit, 9 ... receiving unit, 10 ... ECG unit, 11 ... computer system, 11a ... interface unit, 11b ... data collecting unit, 11d ... storage unit, 11c ... reconstruction unit, 11g ... main control unit, 11f ... input unit, 11e: Display unit.

Claims (19)

Acquisition means for acquiring magnetic resonance data relating to magnetic resonance in the subject for each data line;
Control means for controlling the acquisition means to collect magnetic resonance data for one or a plurality of unit data groups in a collection period determined based on a start time of the subject's cardiac cycle;
Among the magnetic resonance data acquired by the acquisition means, those related to the unit data group acquired at least in part during the invalid period determined based on the end point of the cardiac cycle in which the magnetic resonance data was acquired A determination unit that determines, as invalid data, data related to a unit data group that has been acquired in all periods other than the invalid period,
Means for reconstructing an image relating to the subject using the effective data. Acquisition means for acquiring magnetic resonance data relating to magnetic resonance in the subject for each data line;
Control means for controlling the acquisition means to collect magnetic resonance data for a plurality of data lines in a collection period determined based on a start time of the subject's cardiac cycle;
Among the magnetic resonance data acquired by the acquisition means, data related to a data line acquired at least partially during an invalid period determined based on the end time of the cardiac cycle at which the magnetic resonance data was acquired is invalidated As the data, a determination means for determining as valid data data relating to a data line all acquired in a period other than the invalid period,
Means for reconstructing an image relating to the subject using the effective data.   3. The magnetic resonance imaging apparatus according to claim 2, wherein the determination unit determines the invalid period from a point in time after going back a predetermined invalid time from a reference time phase of the cardiac cycle to the reference time phase. .   The magnetic resonance imaging apparatus according to claim 3, wherein the determination unit sets a time phase in which an R wave is generated in an electrocardiographic waveform related to the subject as the reference time phase.   The magnetic resonance imaging apparatus according to claim 3, wherein the determination unit sets a time obtained by multiplying the cardiac cycle by a predetermined coefficient as the invalid time.   The magnetic resonance imaging apparatus according to claim 2, wherein the control unit controls the acquisition unit to acquire again the magnetic resonance data related to the same data line as the invalid data.   The control means controls the acquisition means to collect magnetic resonance data related to a necessary data line according to a predetermined plan, and after the magnetic resonance data collection in the predetermined plan is completed, the control means The magnetic resonance imaging apparatus according to claim 6, wherein the acquisition unit is controlled to acquire again magnetic resonance data relating to the same data line as invalid data.   The control means controls the acquisition means so as to collect magnetic resonance data related to a necessary data line according to a plan predetermined for each cardiac cycle, and after the acquisition in each cardiac cycle is completed, The magnetic resonance imaging apparatus according to claim 6, wherein the acquisition unit is controlled to acquire again magnetic resonance data relating to the same data line as the data.   The control means controls the acquisition means so that the magnetic resonance data relating to the data line is not collected again when the data line of the invalid data is determined as a data line of low importance. The magnetic resonance imaging apparatus according to claim 6. Acquisition means for acquiring magnetic resonance data relating to magnetic resonance in the subject for each data line;
Control means for controlling the acquisition means to collect magnetic resonance data for one or a plurality of slice encodings in an acquisition period determined based on a start time of the subject's cardiac cycle;
Among the magnetic resonance data acquired by the acquisition means, invalid are those related to slice encoding acquired at least in part during an invalid period determined based on the end point of the cardiac cycle at which the magnetic resonance data was acquired. A determination unit that determines, as valid data, data relating to slice encoding that has been acquired in all periods other than the invalid period,
Means for reconstructing an image relating to the subject using the effective data.   11. The magnetic resonance imaging apparatus according to claim 10, wherein the determination unit determines the invalid period from a point in time preceding a reference invalid phase to a reference time phase from a reference time phase of the cardiac cycle. .   The magnetic resonance imaging apparatus according to claim 11, wherein the determination unit sets a time phase in which an R wave is generated in an electrocardiographic waveform related to the subject as the reference time phase.   The magnetic resonance imaging apparatus according to claim 11, wherein the determination unit sets a time obtained by multiplying the cardiac cycle by a predetermined coefficient as the invalid time.   The magnetic resonance imaging apparatus according to claim 10, wherein the control unit controls the acquisition unit to acquire again the magnetic resonance data related to the same data line as the invalid data.   The control means controls the acquisition means to collect magnetic resonance data related to a necessary data line according to a predetermined plan, and after the magnetic resonance data collection in the predetermined plan is completed, the control means 15. The magnetic resonance imaging apparatus according to claim 14, wherein the acquisition unit is controlled to acquire again magnetic resonance data relating to the same data line as invalid data.   The control means controls the acquisition means so as to collect magnetic resonance data related to a necessary data line according to a plan predetermined for each cardiac cycle, and after the acquisition in each cardiac cycle is completed, 15. The magnetic resonance imaging apparatus according to claim 14, wherein the acquisition unit is controlled to acquire again magnetic resonance data relating to the same data line as the data.   The control means controls the acquisition means so that the magnetic resonance data relating to the data line is not collected again when the data line of the invalid data is determined as a data line of low importance. The magnetic resonance imaging apparatus according to claim 14. Obtain magnetic resonance data about magnetic resonance in the subject for each data line,
Controlling the acquisition to collect magnetic resonance data for a plurality of data lines in a collection period determined based on a start time of the subject's cardiac cycle;
Among the acquired magnetic resonance data, the data related to the data line acquired in the invalid period determined based on the end point of the cardiac cycle in which the magnetic resonance data was acquired is set as invalid data, and other than the invalid period The data related to the data line acquired during the period is determined as valid data
A magnetic resonance imaging method comprising reconstructing an image related to the subject using the effective data. Obtain magnetic resonance data about magnetic resonance in the subject for each data line,
Controlling the acquisition to collect magnetic resonance data for one or more slice encodings in a collection period determined based on a starting time point of the subject's cardiac cycle;
Among the acquired magnetic resonance data, the data related to the slice encoding acquired at least in part in the invalid period determined based on the end point of the cardiac cycle in which the magnetic resonance data was acquired is used as the invalid data, It is determined that valid data is related to slice encoding that is acquired in all periods other than the invalid period.
A magnetic resonance imaging method comprising reconstructing an image related to the subject using the effective data.

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